Stress shadow effects and microseismic events during hydrofracturing of multiple vertical wells in tight reservoirs: A three-dimensional numerical model

Abstract

Optimizing hydrofracturing schemes for multiple vertical wells is crucial for developing complex fracture networks that facilitates the transport of unconventional hydrocarbon resources in tight reservoirs. The stress shadow effect that occurs between multiple wells has a significant effect on the development of fracture networks. However, the influence of fracturing schemes, including fracturing sequences and well spacing, on stress shadow effects are poorly understood. In this study, a three-dimensional (3D) numerical model based on actual reservoir data was developed to explore these influences. The simulation considers hydromechanical coupling and leak-off effects and employs the adaptive finite element–discrete element method to achieve high-precision solutions and reliable 3D fracture propagation paths. Typical fracturing cases were simulated to address the differences between sequential and simultaneous fracturing, the effects of different well spacing in sequential fracturing, and the optimization of the number of multiple vertical wells required to maximize fracturing efficiency. Our results indicate that the 3D fractured areas produced in simultaneous fracturing are much smaller than those produced in sequential fracturing. For sequential fracturing, the fractured areas of three vertical wells were larger than the fractured areas of five vertical wells. In the sequential fracturing of three wells, the fractured areas were almost unchanged because the well spacing was large enough to sufficiently weaken the stress shadow effect, thus inducing almost constant fractured areas in each fracturing sequence. Using the computed stress difference and fractured areas, we defined an area ratio to quantify the stress shadow effect, which reflects the feasibility of various fracturing schemes. It is easier to induce more microseismic events during simultaneous fracturing than during sequential fracturing, and the cumulative magnitude of simultaneous fracturing is higher; furthermore, the cumulative magnitude of sequential fracturing of the three wells was lower than that of the five wells, reflecting weak stress shadow effects.